The present invention relates to a communication system.
Communication networks with communication systems at their nodes exist for the "voice" communication service. Their task is to establish connections between the subscribers connected to the communication systems. It is possible to draw a distinction here between public communication networks and so-called local area networks which are primarily installed within companies. Up to several thousand subscribers can be connected to the communication systems situated in the nodes of the local area networks, which are often referred to as private branch exchanges. An interface to the public communication networks also permits communication with external partners.
As long as communication is oriented to the "voice" form of communication, analog communication networks and communication systems are adequate for the associated basic functions. Modern office communication, however, encompasses further forms of communication which cannot be realized, or realized only inadequately, with such analog systems. These are the "image", "data" and "text" forms of communication for which digital methods are used for transmission and processing. In practice, therefore, from time to time digital communication networks have resulted that were set up parallel to the hitherto existing analog communication networks. Of necessity, this entails a certain complexity and degree of confusion as far as communication with other subscribers is concerned, since in general different subscriber numbers for the different communication services are assigned to a subscriber. This was one of the reasons for integrating the parallel networks in a uniform communication network.
The ideas surrounding this concept are associated with the term ISDN (Integrated Services Digital Network). In public communication networks the realization of these concepts is still in a period of transition, while the integration of the services in the office has already progressed further. These types of digital communication systems which permit flexible adaptation to modern forms of organization are known from the publication "ISDN im Buro" (ISDN in the office), published in December 1985 as a special issue together with the monthly publications `Telcom Report` and Siemens magazine "COM" from the Siemens company. This is accomplished, inter alia, by integration of so-called servers, that is to say hardware modules, which provide special services - features in the communication system - by means of system procedures. Said servers are used for the transmission of image data, text data, etc.
In certain application areas for office communication, special features that are not generally common are required; one such application area is for instance international trading with shares, currency, raw materials, which requires not only worldwide communication for decision-making but also direct, active intervention in the market. Special systems for such purposes are currently connected as independent systems or as secondary private branch exchanges under an analog main system.
The digital communication systems discussed in the abovementioned publication are therefore not designed specifically for such applications; thus, for instance, for an exchange dealer who needs to react to a changing market situation in seconds, not only constant monitoring of the market, but also active intervention in the market is vital. Appropriate features for this are provided by known digital communication systems only to a limited extent, and by known analog communication systems only with a relatively high outlay, for example by means of a secondary private branch exchange in addition to the analog main system.
That any member of an exchange dealing team can be reached quickly, to process a standard job for example, is often of particular importance, as is the capability of setting up conference calls.
An ISDN communication system is furthermore known from Telecom Report, "Integrated Services Digital Network", Volume 8, 1985, Gunter Raab: "Private ISDN Communication Systems and Interoperation with the Public ISDN" and from German reference 3,625,857. Several services can be combined under one telephone number with communication systems designed in such a way. Such communication systems are not, however, designed for special applications.